Feb 28 2011
CyberOptics Semiconductors has published an application note on its web site discussing how its WaferSense® Vibration and Leveling Sensors helped a vertical diffusion group characterize various causes of wafer damage that occurred during high‐volume processing of wafers in a boat.
Wafer breakage, micro scratching and particle contamination were reducing yield in a fab’s 200 mm high volume process. Misaligned wafers in crowded cassettes and tool vibration created by environmental forces, including fans, failing robotic components and carts moving along the aisle’s perforated floor were suspected causes of reduced yield. Wafers were vulnerable to damage during high volume handling at the load port, in the cassettes with narrow pitch and as they ascended a long Z axis and were exposed to the hot furnace.
Placing a WaferSense Vibration Sensor and Leveling Sensor in the same cassette, the fabricator conducted a series of tests, comparing the same tool movements at different locations in the process to characterize wafer damage causes.
A wireless and wafer like inclinometer, the WaferSense Auto Leveling Sensor captures the inclination of previously out-of-reach semiconductor process equipment. Unlike traditional methods, the Auto Leveling Sensor doesn't require equipment disassembly or disruptions to vacuum chambers, reducing calibration time by 80% or more. The WaferSense Auto Vibration Sensor moves through semiconductor process equipment to monitor three-axis accelerations and vibrations. A wafer-like shape is compatible with existing automation and wireless communications provide real-time data to speed tool setup and maintenance.
For the 200mm fab analysis, the vacuum‐compatible sensors measured wafer vibration in x, y and z dimensions and wafer tilt in x, y dimensions while cassettes moved throughout wafer‐handling stations in the diffusion process: from the load port to the CZ stage, from storage rack to transfer rack and into the cooled furnace. Wafer tilt and vibration also were measured in a storage rack with the fan on and off and as engineers ran carts at various speeds and weights in the aisle next to storage and transfer racks.
The real‐time data from the wireless sensors on tool vibration and leveling allowed engineers to make immediate adjustments and re‐characterize the diffusion process. Co‐planarity established among wafer‐handling stations ensures proper wafer tilt in cassettes and prevents wafer damage throughout the process.
Source: http://www.cyberopticssemi.com/